Anechoic areas, also called fluid dark areas, are commonly found in liquid substances, abnormal body fluids, liquefied necrosis, echogenic cystic structures in the uterine cavity, etc. They are usually benign. 1. In normal tissues, such as urine in the bladder, bile in the gallbladder, blood in the blood vessels, etc., there are liquid substances, at this time, ultrasound examination is generally unable to reflect, shown as a non-echoic area. 2. In abnormal cases, such as pleural fluid, ascites, blood accumulation, pus accumulation and other liquids appearing in normal areas, ultrasound shows anechoic area, at this time, we should be alert to the presence of malignant tumors, and we need to improve the relevant examinations to identify benign and malignant. 3. In benign or malignant nodules, liquefaction necrosis may appear, and ultrasound also shows anechoic area, which requires further pathological examination to determine the benign or malignant nature. 4. If the yolk sac is not formed in early pregnancy, ultrasound will show anechoic cystic structures in the uterine cavity, which is not a sign of malignancy, and should be rechecked after a period of time. In conclusion, ultrasound shows anechoic areas, should improve the relevant examination, clear diagnosis, in the doctor’s guidance for the next step.